Pump unloader



April 1938.- j a. s. AIKM N 2,115,546

' PUMP UNLOADER Y Filed pct. 19. 1934 39 40 q 4442 3 5/ 46 4 F g.1.

57 56 v U 65 -54 a INVENTOR BURTON SAIKMAN Patented Apr. 26, 1938 PATENT OFFICE PUMP UNIDADER Burton Aikman, Wilkinsburg, Pa., assignor to The Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application'october 19, 1934, Serial No. 749,020

(llaims.

This invention relates to fluid compressors and more particularly to means for automatically unloading a fluid compressor.

It is an object of this invention to provide a I g fluid compressor with an unloader adapted to unload the compressor when the speed thereof is reduced to a predetermined value and to maintain the compressor unloaded while starting, until the speed has increased to a predetermined value, so as to permit the driving unit, which may be an electric motor or an internal combustion engine, or any preferred prime mover, to pick up speed before the work of compressing begins.

Another object of the invention is to provide a fluid compressor and unloading means which operates to unload the compressor when same is stopped, by opening communication from the compression chamber of the compressor to the m atmosphere and which operates to maintain said communication open while starting, until the speed of the compressor is increased to a predetermined value, so that only a low starting torque is required of the driving unit. a as A further object of the invention is to provide an unloader for a fluid compressor wherein the unloader valve is actuated by the fluid lubricant of the lubricatingsystem and is responsive to variations in the pressure of the fluid lubrillt cent, and wherein the pressure of thefluid lubricant is regulated by centrifugally controlled means, so that loading 01 the compressor is accomplished when the speed of the compressor attains a predetermined value.

35 Other objects and advantages will appear from the following more detailed'description of the invention. I

In the accompanying drawing, Fig. 1 is a diagrammatic view, mainly in section, of a fluid compressing apparatus embodying my inven- The air compressor may comprise a crank case.

4 having a crank chamber 5, a cylinder casing 5 having a compression chamber 1 containing a piston 8, and a cylinder cover 9 closing the com- 5 presslon chamber I.

The piston 8 is connected, in-the usual manner, by a connecting rod II! We crank pin ll provided on the crank shaft l2, which is journaled in bearings l3 and I4 mounted in end plates l5 and I6 secured in anydesired manner to the 5 side walls of the crank case. A suitable gasket, such as I1, is clamped between each said end plate and the side walls of the crank case to provide a tight joint. The crank shaft I2 is adapted to be connected to a prime-mover, such 10 as an electric motor or an internal combustion engine. v l

The cylinder covert contains an inlet chamber 39 from which air is drawn at atmospheric pressure past the inlet valve disc lll into the 15 compression chamber l'upon the suction stroke of the piston 8. The inlet valve disc 40 is-yieldingly retained upon its seat by means of a spring 4|. The cylinder cover 9 also contains an outlet chamber 42 which is adapted to receive fluid under pressure compressed in the compression chamber l and forced pastthe discharge valve disc 43 which is yieldingly pressed to its seat by means of a spring M,

The check valve device 3 may comprise a casing containing a valve disc t5 having at one side a chamber 46 connected by pipe 41 to the storage reservoir 2 and at the other side a chamber W connected by a pipe 49 with the outlet cham-' ber 42 in the cylinder cover 9 of the compressor ,and also connected by a pipe 50 with the chamber 37 associated with the unloader valve 36. which will be referred to more in detail hereinafter. The valve disc i5 is yieldingly pressed toits seat by a spring 5! contained in the chamber It and is adapted to prevent back flow from the storage reservoir to chamber 31, for a reason which will be understood from the description hereinafter.

The fluid lubricating system of the compressor comprises a pump which may include a rotor [8 that is formed on the crank shaft II by enlarging a portion thereof, intermediate the bearing l3 and the crank pin ll, concentric with the axis 4 of said shaft. The rotor is enclosed in a cylindrical chamber. I 9 which may be formed in an extended portion of the end plate l5, said chamher being disposed eccentrically with respect to .the rotor It.

The rotor lt is provided with a through slot 20 disposed diametrically thereof in whlch are slidably received rotor blades 2| and 22 which are adapted, at their outer ends, to bear against the interior wall of the cylindrical chamber is and which are provided with bores 23 and 24,

respectively, extending axially of said blades from the innerends thereof. Thus, with the blades assembled in the slot 25, the bores 22 and 24 are axially aligned and the open ends thereof face each other. A coil spring 25, secured at one end to a pin 28 carried by the blade 2| at the bottom of the bore 22 and secured at the other end to a pin carried by the blade 22 at the bottom of the bore 24, is under initial tension therebetween and acts to maintain said blades in their innermost position, as will now be seen.

For limiting the sliding movement of the blades 2| and 22 inwardly, a stop pin 28 is provided which is screw-threaded into an opening in the rotor disposed radially thereof and at right angles to the axis of the slot 2|), the pin 25 being preferably of such length that it extends across said slot. with the blades 28 and 2|, the spring 25 and the pin 28 assembled in the rotor I8, said pin separates said blades, and the spring 25, being under initial tension between said blades, acts to hold the inner ends thereof in engagement with said pin, so that the blades are held in their innermost position, until the speed of the crank shaft has increased to such a value that the centrifugal force developed thereby and acting on the blades is sufllcient to overcome the tension of the spring 25, as will be understood from the description hereinafter.

The rotor chamber II is provided with an opening 30 which leads to an oil inlet passage II which communicates with a pipe 22 having one end extending into the fluid lubricant 82 at the bottom of the crank case 5. Said chamber is provided with an outlet port 34'which opens into a chamber 35 at one side of an unloader valve piston 38.

Theunloader valve" piston 28 is contained in the casing of the extended portion of the end plate l5 and has at one side the chamber 25 which, as above mentioned, is connected through the port 34 with the rotor chamber I8, and has at the other side a chamber 31 which is in continuous communication with the crank chamber 5 through the opening 35. The valve piston 38 controls communication from the pipe 50, which leads to the chamber 48in the check valve device 2, to the chamber 31 and thereby controls communication from the outlet chamber 42 of the compressor to the crank chamber 5. The flow capacity of the opening 38 is restricted as compared with the capacity of the communication, including the pipe 50, from the outlet chamber 42 to the crank chamber 5.

A passage 52 leads from the outlet port 34 of the rotor chamber iii to the bearing II for conducting fluid lubricant to said bearing and for conducting fluid lubricant from said bearing to the other crank shaft bearing l4 and to the connecting rod bearing on the crank pin li, a drilled passag 53 is'provided in the crank shaft l2, ex-

tending longitudinally thereof from the bearing l3 to the bearing I4 and having a branch leading to said connecting rod bearing.

A relief valve is interposed between the chamber 35 and the passage 2| and comprises a valve 54, subject on its seating side to the pressure of the fluid lubricant in said chamber and pressed to its seat by means of a spring 55.

When the compressor is idle, the blades 2| and 22 occupy the positions shown in Fig. 1, the tensi'oned spring 25 acting to hold the inner ends of said blades in engagement with the stop pin 28 and thereby out of engagement with the interior wall of the rotor chamber l9. when the compressor is started and until a predetermined'speed of rotation of the crank shaft is attained, the centrifugal force developed thereby and acting on the blades 2| and 22 is insuilicient to cause said blades to move outwardly in the slot 20, against the tension of the spring 25, into engagement with the interior wall of the rotor chamber l9 and there is, therefore, no fluid lubricant pressure acting in chamber 35 at the left of the unloader valve piston 38. Atmospheric air drawn into the compression chamber 1 of the compressor past the inlet valve disc 40 is discharged past the discharge valve 43 into pipe 49 and is forced thence through chamber 48 in the check valve device 3 and pipe 50. There being no fluid lubricant pressure acting in chamber 35 when the compressor is initially started, if the valve piston 36 is not already in its open position, it will be moved inwardly to that position by the pressure of the fluid discharged into the pipe 50, this movement being effected promptly and positively, due to the fact that the unseating of the valve piston exposes the full area thereof to the pressure of said fluid and also to the fact that the opening 38, being restricted, permits a rapid build up of fluid pressure in chamber 81. With the valve piston 38 unseated, fluid discharged into pipe 50 flows therefrom to the atmosphere past said valve piston, through chamber 31, the opening 38, the crank chamber 5, the oil filling inlet 58, and openings 51 in the cover 58. With the compression chamber 1 of the compressor thus vented to the atmosphere on the compression stroke, the compressor is unloaded and it therefore quickly picks up speed. During this time, back flow of fluid under'pressure from the storage reservoir 2 through the check valve device 3 is prevented by the valve disc 45 which is held seated by the pressure of the reservoir fluid in chamber 48.

When the speed of rotation of the crank shaft I2 has increased to a predetermined value, the centrifugal force acting on the blades 2| and 22 overcomes the tension of the spring 25 and said blades are moved outwardly within the slot 20 under the action of said force into engagement with the interior wall of the rotor chamber i9. Due to the wellknown action of the blades, fluid lubricant is pumped from the body of fluid lubricant 33 into chamber 35 through the pipe 32, passage 3|, inlet opening 30, chamber i9, and outlet passage 34. The fluid lubricant pressure in chamber 25 increases until the valve piston 36 is moved rightwardly thereby, to its seated position against the pressure of the fluid delivered into chamber 21 from the compression chamber I. The vent connection of the compression chamber is thus cut off and the pressure of the fluid discharged from said chamber into the pipe 49, and thence into the chamber 48 of the check valve device 3, will increase until the valve disc 45 is unseated thereby, and flows thence through pipe 41 into the storage reservoir 2. Thus, the loading of the compressor iseffected only after the crank shaft attains a predetermined speed of rotation.

, Fluid lubricant delivered to the passage 34 is also forced therefrom through passage 52 to the crank shaft bearing l3 and from thence into passage 53 in the crank shaft i 2, from whence it is forced to the bearing of the connecting rod III on the crank pin (and to the bearing l4. c When the pressure of the fluid lubricant delivered by the pump to chamber 35 exceeds a predetermined degree, the relief valve 54 will be unseated thereby against the action of the spring 55 and fluid lubricant will then flow from said chamber to the passage 3!,thereby preventing the building up of excessive pressure in the fluid lubricant circulating system.

When the compressor is stopped and the speed of the crank shaft has fallen to a predetermined degree, the tension of the spring will overcome the centrifugal force acting on the blades 2| and 22 and said blades will be moved inwardly within the'slot 20 out of engagement with the interior wall of the rotor chamber i8 and into engagement with the stop pin 28. With the blades thus retracted, the fluid lubricant pump becomes ineifective. The pressure of the fluid lubricant in chamber acting to hold the valve piston 36 seated being thus relieved, fluid under pressure in pipe will unseat said valve piston,

causing the compression chamber I of the compressor to be vented'to the atmosphere in the manner hereinbefore described. Thus, the compressor is unloaded when brought to rest, and it is apparentthat upon initial starting of the compressor,'the only load on the compressor, to long as the fluid lubricant pump remains ineffective, will be the compression of the fluid at atmospheric pressure within the compression chamber 1.

The speed of rotation of the crank shaft I! at which the compressor loaded is determined by the initial tension of the spring 25, and thus the compressor may be loaded at any desired speed of operation.

The loading of the compressor being dependent upon the pressure of the fluid lubricant while the compressor is operating, it is obvious that in compressor.

From the foregoing, it is apparent that an unloading mechanism for a fluid compressor has been provided which is controlled by the pressure of the fluid lubricant of the lubricating system and which is responsive to the speed of the compressor.

While one illustrative embodiment of the inby said compressor is discharged, said valve being subject to theopposing pressures of the fluid discharged by said pump and fluid compressed by said compressor into said communication and being adapted to be operated by the fluid discharged by said pump to close said communication and thereby load said compressor and adapted to be operated upon the relief of fluid under pressure discharged by said pump to open' said communication and thereby unload said compressor, said pump being rendered ineffective to supply fluid 2. A control mechanism for a fluid compressor comprising a fluid pump operative to supply fluid under pressure, and a valve for controlling a communication through which fluid compressed by said compressor is discharged, said valve being subject to the opposing pressures of the fluid discharged by said pump and fluid compressed by said compressor into saidcommunication and being adapted to be operated by the fluid discharged by said pump to close said communication and thereby load said compressor and adapted to be operated upon the relief of fluid under pressure discharged by said pump to open said communication and thereby unload said compressor, said pump being rendered operative by the action of centrifugal force to supply fluid under pressure to said valve for loading said compressor when the speed of the compressor exceeds a predetermined speed and being rendered inoperative, by the' action of centripetal force, to supply fluid under pressure to said valve, and thereby efiect unloading of said compressor, when the speed of said compressor is less than said predetermined speed.

3. The combination in a fluid compressor coniprlsing a casing having a crank case chamber containing a supply of fluid lubricant, a crank shaft rotatable in said crank case chamber, means operative by fluid lubricant pressure for effecting the loading of said compressor. and means for supplying fluid lubricant under pressure to said loading means, comprising a pump having a casing provided with a rotor chamber, a rotor element rotatably mounted in said chamber eccentrically thereof and operated by said crank shaft and having a plurality of radial slots therein, a member slidably mounted in each of said slots and movable, by the action of centrifugal force, into engagement with the interior wall of said rotor chamberfor supplying fluid lubricant under pressure from said crank case chamber to said loading means when the speed of said crank shaft exceeds a predetermined speed, and means for rendering said members ineffective when the speed of said crank shaft 'is less than said predetermined speed.

4. The combination in a fluid compressor comprising a casing having a. crankcase chamber containing a supply of fluid lubricant, acrank. shaft rotatable in said crank case chamber, means operative by fluid lubricant pressure for effecting the loading of said compressor, and

means for supplying fluid lubricant under pres- 1 sure to said loading means, comprising a pump having a casing provided with a rotor chamber, a rotor element rotatably mounted in said chamber 'eccentrically thereof and operated by said crank shaft and having a plurality of radial slots therein, a member slidably mounted in each of gal force, into engagement with the interior wall of said rotor chamber for supplying fluid lubricant under pressure from said crank case cham-- ber to said loading means when the speed of said crank shaft exceeds a predetermined speed, and yielding means acting on said members whereby said members are maintained out of engagement with the interior wall of said rotor chamber against the action of centrifugal force when the speed of said crank shaft is less than said predetermined speed.

5. In combination, a reservoir, 9. control chamber, a fluid compressor having a compression chamber, the compressor being adapted to comsaid slots and movable by the action of centrifutrol chamber, a lubricating system. for supplying lubricant under pressure to portions of the compressor, and means responsive to the pressure of the lubricant in said system for controlling the release of fluid from said control chamber.

BURTON 8. Am. 

